1. Field of the Invention
This invention relates generally to a method of coating various substrates with deposits of amorphous boron carbide, to uses of the coated substrates, and to articles of manufacture thus produced from the coated substrates. It relates in particular to coating cloth substrates.
Amorphous (i.e., substantially non-crystalline) boron-carbon deposits, either in the form of boron carbide or in non-stoichiometric mixtures of boron and carbon, are known to possess desirable mechanical properties, for example very high tensile strength and modulus of elasticity. Previously, in order to produce boron-carbon deposits by chemical vapor deposition (i.e., CVD), temperatures well above 1100.degree. C. usually have been required. At such temperatures the deposits are usually crystalline. These high temperatures also destroy or cause degradation of many substrate materials and at such temperatures the individual filaments making up the fibers of a cloth cannot be uniformly coated. Only the outer, not inner, portions of the cloth would be coated, and the cloth would be canned. Thus, it has been a problem to obtain high quality deposits, and particularly at economical speeds.
2. Prior Art
In U.S. Pat. No. 3,537,877, Reeves et al., amorphous boron-carbon deposits were produced by contacting a heated substrate material with a gaseous mixture of acetylene and a boron hydride at a relatively low temperature and pressure. That process has the serious disadvantage, however, that boron hydride (a borane) is a very toxic substance. Thus, its use in a reaction is undesirable. That patent furthermore does not teach or suggest hot-pressing multiple layers of coated cloth, nor does it teach a method of controlling the ratio of B:C in boron-carbon deposits.
Leclerq et al., U.S. Pat. No. 3,846,224, Wainer et al., U.S. Pat. No. 3,269,802, and Bauer, U.S. Pat. No. 3,994,248, do not even address (much less solve) the problem of canning. Thus, those patents do not lead one to a method of coating a cloth with boron carbide so that all of the tiny yarn filaments making up a yarn bundle are substantially uniformly coated. In order to avoid canning, both a low temperature and a low pressure must be used; and such a dual requirement is not taught in those patents. Leclerq et al. furthermore coats a single filament, not a multifilamentary yarn as in the present invention; and in that patent in the preferred coating temperature range (1150.degree.-1300.degree. C.), canning would definitely occur. Additionally in Wainer et al., the reactants are different from those used in the present invention, in Wainer a carbon substrate reacting with a halide in the absence of a hydrocarbon gas so as to form a carbide.
Turkat, U.S. Pat. No. 3,294,880, Bourdeau, U.S. Pat. No. 3,369,920, Bourdeau, U.S. Pat. No. 3,334,967, and Basche, U.S. Pat. No. 3,464,843, all employ high temperatures (at least 1300.degree. C.) in their coating reactions. As noted above, at these temperatures canning would occur.
Additionally, none of the patents cited above nor any other known reference teaches a method for controlling the atom ratio of B:C in boron carbide deposits. And no other reference teaches hot pressing of cloth which has been uniformly coated with boron carbide as in the present invention.